5.1 TURNING OPERATIONS

Metal removal from cylindrical parts is accomplished using standard types of engine lathes or modern machining centers, the latter operated by computer numerical control (CNC). Figure 5.1 shows a typical large geared-head engine lathe with a digital two-axis readout panel at the upper left of the machine. Figure 5.2a shows a modern high-speed CNC machining center. The machining center is capable of highly accurate and rapid production of machined parts. These modern machining centers are the counterparts of engine lathes, turret lathes, and automatic screw machines when the turned parts are within the capacity or rating of the machining center. Figure 5.2b shows a view of the CNC turning center s control panel.

Cutting Speed. Cutting speed is given in surface feet per minute (sfpm) and is the speed of the workpiece in relation to the stationary tool bit at the cutting point surface. The cutting speed is given by the simple relation

and

where S = cutting speed, sfpm or m/min

d _f = diameter of work, in or mm

rpm = revolutions per minute of the workpiece

When the cutting speed (sfpm) is given for the material, the revolutions per minute (rpm) of the workpiece or lathe spindle can be found from

Figure 5.1: A typical geared-head engine lathe.

Figure 5.2a: A modern CNC turning center.

and

EXAMPLE. A 2-in-diameter metal rod has an allowable cutting speed of 300 sfpm for a given depth of cut and feed.